1. Field of the Invention
The present invention relates to a novel resin composition obtained by compounding a thermoplastic resin composition with poly(phenylene ether), which gives molded articles excellent in heat resistance, impact resistance, surface gloss, painting, and thermal stability.
2. Description of the Related Art
Poly(phenylene ether) is widely known as a resin excellent in heat resistance, mechanical and electrical properties. This resin, however, is used seldom alone but mostly in combination with polystyrene or rubber-modified polystyrene for forming a modified resin, because of its low imact resistance, insufficient processability, and unsatisfactory chemical resistance. Since the modified poly(phenylene ether) is excellent in heat resistance, mechanical and electrical properties, and processability, it is widely used in automotive parts, office appliances, electric appliance parts, and the like.
Since the rubber-modified polystyrene is produced generally by the bulk-suspension polymerization of the monomeric styrene containing a rubber-like polymer dissolved therein, it is necessary to limit the concentration of the polymer to a certain range which is favorable for the phase transition in view of the solution viscosity. Accordingly, the amount of the rubber-like polymer is preferably about 10% by weight or less based on the weight of the rubber-modified polystyrene. A composition comprising the rubber-modified polystyrene of such a recipe and the poly(phenylene ether) does not exhibit a sufficient impact resistance and, as a consequence, the molded article tends to break at the corner or thin wall portion at the time of being released from the mold. A rubber-like elastomer is, therefore, incorporated in the composition to improve the imact resistance. Even in this case, the resulting composition is not sufficient in impact strength and, in addition, tends to discolor upon heating, and is inferior in processability.
Furthermore, a composition consisting of a rubber-modified polystyrene and a poly(phenylene ether) gives a molded product which has disadvantages that surface gloss is inferior, such phenomena as cracking, crazing, absorption (the coating surface is unevenly colored) and the like tend to be caused at the surface when the molded article is coated, and painting is inferior.
The styrene-acrylonitrile copolymer and the rubber-like polymer-styrene-acrylonitrile copolymer (ABS resin) are widely used as resins excellent in painting, solvent resistance, impact resistance, and processability. However, these resins generally contain 20 to 30% by weight of acrylonitrile and, as a consequence, are unsatisfactory in compatibility with poly(phenylene ether); the blend, therefore, gives molded articles generally unsatisfactory in appearance, impact resistance, heat resistance, and painting.
The modified poly(phenylene ether) has high heat resistance and hence is molded at high temperatures. Therefore, the modified polyphenylene ether is required not to cause deterioration of physical properties when molded at high temperatures. However, in fact, the impact resistance thereof is greatly deteriorated when it is molded at high temperatures (hereinafter referred to as thermal stability).
Various means have been proposed to eliminate the above-noted disadvantages of the modified poly(phenylene ether). For instance, Japanese Patent Publication No. 8,139/82 discloses a blend of a methyl methacrylate-modified ABS resin and a poly(phenylene ether). Such a blend, however, is poor in thermal stability and is commercially unfavorable owing to an increase in cost resulting from the high cost of methyl methacrylate. Japanese Patent Publication No. 40,046/73 discloses a heat resistant resin blend obtained by blending a styrene-acrylonitrile copolymer having an acrylonitrile content smaller than that of a generally available copolymer and a poly(phenylene ether). The resulting resin blend, however, is not sufficiently improved in heat resistance and solvent resistance. The molded articles made from both resin blends described in the above two patent publications are also unsatisfactory in surface gloss and painting.
There is also proposed a composition comprising a poly(phenylene ether) and a styrenic resin having a large alkenyl cyanide compound content which has added thereto a specific amount of a styrenic resin containing a small amount alkenyl cyanide compound. Such a composition, however, is still unsatisfactory in painting and thermal stability.